First of all, I'll reiterate a key phrase in that video "If you learned a lot from the previous segment, turn your ears off for this next part."

But ... what he's talking about is changing the disc's angle by changing the plane you're delivering the disc on. If you were watching from behind, the first 10 minutes you would see his body as an "|". The next 5 or so minutes, it would look like a "/" to change to a more anhyzer disc angle, or "\" to change to a more hyzer disc angle.

For the question in the vid "Why would you change half-way through your throw": Because it's not comfortable to run up with your body like "/". It's also more disorienting on reachback.